I. Eye Development

Sara Thomasy DVM, PhD, DACVO

 Morphogen from the hedgehog family . Encoded by the SHH gene  Regulates vertebrate organogenesis . Limb patterning . Midline structures in the brain . Spinal cord . Thalamus . Teeth  Veratrum californicum . Day 14 of gestation in sheep  Steroidal alkaloids . Cyclopamine and jervine . Inhibits SHH

Corn Lily or False Hellebore

 Paired box protein Pax-6 . Encoded by the PAX6 gene  Transcription factor in development . 2 binding sites that interact with DNA . Brain & eye  Master control gene in eye development . Highly expressed in retina, lens and cornea  Controls position of eyes on body plan  Highly conserved across Bilateria

 Aniridia  Gillespie syndrome  Peters anomaly  WAGR syndrome  Canine model of aniridia – Is PAX6 the cause? . 15 affected & 6 unaffected Spanish Catalan sheepdogs  No pathological mutations in the affected dogs  Canine PAX6 highly homologous with human

Hunter et al. Mol Vis. 2007 ;13: 431-42.  Congenital cataract in wire-haired Dachshunds . 17 candidate genes (BFSP2, EYA1, FOXE3, FTL, GCNT2, GJA3, GJA8, HSF4, MAF, MIP, PAX6, PITX3, SIX5, SORD, SOX1, SPARC, TRNT1) . 15 affected & 6 unaffected dogs  No significant linkage/association ID

Muller C & Disti O. Vet J. 2009 ;182: 342-5.  Forkead box protein E3 . Encoded by the FOXE3 gene . AKA forkhead-related transcription factor 7  Transcription factor in development . Highly expressed in the lens . Presumptive midbrain  Expression uniform: . Lens placode . Lens vesicle  Confined to anterior lens epithelium during fiber differentation  Dominant → read through of stop codon → protein extension . Anterior segment dysgenesis . Congenital cataract  Recessive → missense, frameshift, nonsense mutations . Aphakia . Microphthalmia . Sclerocornea  Deficiency = dysgenic lens phenotype . Microphthalmia . Corneal opacity . Small & irregular lenses . Lenticular-corneal adhesion . No systemic features  Rinshoken cataract (rct) recessive mouse phenotype . Upstream deletion of FOXE3 . Microphthalmia . Cataract  SRY (sex determining region Y)-box 2 (aka SOX2) . Encoded by the SOX2 gene  Transcription factor in development . High mobility-group box domains to bind DNA . Pluripotency of undifferentiated embryonic stem cells  Cooperates with Pax6 in lens development  Initiates morphogenesis in the optic cup  High expression in: . Lens . Retina  Anophthalmia  Microphthalmia  Colobomatous microphthalmia  Coloboma  Cells cultured from brains dissected of 45-day old feline fetuses . Expressed nestin, SOX2, Ki-67, fusin & vimentin  Surgically implanted in 5 dystrophic Abyssinian cats . Survived in 3/5 cats

 Silver dapple gene (PMEL)  Chocolate coat + flaxen mane & tail  Missense mutation in exon 11 of premelanosome protein  Genetic test (UC Davis VGL)  MCOA – Incomplete dominant  Heterozygous – less severe cyst phenotype  Homozygous – wide range of anomalies  Multiple breeds  Rocky Mountain Horse  Kentucky Mountain Saddle Horse  Icelandic Horse  Morgan Horses AnderssonDogLG, et al. PloS One. 2013 ;8: e75639Dog.  Cornea globosa  Abnormal pectinate ligaments  Iris & corpora nigra hypoplasia  Congenital miosis  Temporal iris & ciliary body cysts  Retinal cysts  “High-water marks” – focal detach/reattach  Retinal dysplasia or detachment  Cataract  Lens luxation

 5 unrelated ponies – phenotyped & genotyped . 1 heterozygote – temporal ciliary cysts only . 4 homozygotes ▪ Cornea globosa (n = 3) ▪ Iris hypoplasia (n = 3) ▪ Cataracts (n = 4)  5 unrelated ponies – phenotyped & genotyped . 4 silver dapple or chocolate coat color ▪ Flaxen mane & tail . 1 palomino ▪ Masks silver dapple coloring ▪ Homozygous at MCOA locus  67 Comtois & 18 Rocky Mountain horses . Carrier vs noncarrier – coat color or genetic testing . 88% had at least one copy of the Silver mutant allele . Carriers: ▪ US detected cysts not visible in 70% ▪ ↑ AC depth ▪ ↓ Iris thickness

 Merle gene  Mottled color patches within a solid coat  SINE insertion into PMEL  Genetic test (IDEXX)  Double merles (mm)  Predominantly white coat  Eye defects  Deafness

Dog Dog  Multiple breeds  Australian Shepherd  Great Dane  Dachshund  Shetland Sheepdog

Dog Dog  Decreased pigment within outer cup  Failure to induce overlying neural crest  Microphthalmia  Iris hypoplasia  Corectopia  Congenital miosis  Dyscoria  Decreased pigment within outer cup  Failure to induce overlying neural crest  Microphthalmia  Iris hypoplasia  Corectopia  Congenital miosis  Dyscoria  Iris coloboma  Cataract  Choroidal hypoplasia  Staphyloma  Hereditary phenotype in Alaskan Huskies:  Polyneuropathy  Ocular abnormalities  Microphthalmia  PPMs  Cataract  Neuronal vacuolation  RAB3GAP1  SINE insertion → Exon 7  Altered transcript  Model for WARBM1 Choroidal hypoplasia ONH coloboma  Abnormal fissure closure  Failure of RPE to induce choroid &/or sclera  Primary lesions:  Choroidal hypoplasia  Posterior polar colobomas  Retinal detachment  Hyphema  Large deletion (7.8 kb) in NHEJ1 gene  Autosomal recessive  Explains choroidal hypoplasia (CH)  Genetic test (Optigen)  Multiple breeds (Incidence in USA of CH)  Rough & Smooth Collie (67%)  Border Collie (2.2%)  Shetland Sheepdog (0.39%)  Australian Shepherd (0.22%)  No association with coat color

Dog Dog  Compliance between clinical & genetic diagnosis  2 breeds: Danish Rough Collie & Shetland Sheepdog  Clinical exam < 10 weeks of age  Genoyping for the NHEJ1 deletion  Poor correlation for the Collies . 10 dogs (del/del) were unaffected  Good correlation for the Sheepdogs

The NHEJ1 locus may be a marker rather thanDog the causative mutationDog  CEA identified in a young female Hokkaido dog  NHEJ1 deletion found  16 other dogs tested . 12 heterozygotes (wt/del) . 4 homozygotes (wt/del) . Phenotyping not performed Copyright © by American College of Veterinary Pathologists

K. Uchida et al. Vet Pathol 2006;43:1017-1021 Japanese Black Cattle  Autosomal recessive  WFCD1 mutation  1 nucleotide insertion → frameshift mutation → stop codon  Small secretory protein  Multiple ocular defects  Microphthalmia  Retinal detachment  Persistent hyaloid artery  Lens abnormalities  Send us samples!  Severe, bilateral cases!  Controls ≥ 10 years of age with normal STT  We pay for shipping  Send us samples!  Affected BTs, GSHPs, or GWHPs  We pay for shipping  Send us samples!  Affected:  Dachshunds  Brittanys  Miniature Schnauzers  Pugs  We pay for shipping